It is often necessary to be able to control the motor of a crane or an equivalent lifting apparatus from several locations In this case, care must be taken that only one control location is active at a time and that an operation once started can be completed without being influenced by another operator.
The motor is generally controlled by means of push-button controllers which select the direction of motion, and the length of time during which the push-button switch is closed determines the speed reference for the motor control system. An alternative is the joystick controller, in which the joystick position determines both the direction and the speed reference value. Push-button controllers are typically used in hanging controllers, which are located near the load to be lifted, whereas joystick controllers are commonly used in the control cabin of a crane.
The mode of operation (i.e. push-button or joystick) is typically selected by means of a separate selection switch, which can be placed, for example, in the control cabin In addition to the selection switch, the cabin must be provided with appropriate wiring for the selection signal, and the motor controller must be provided with an extra input for this purpose.